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Grind moon and pour spin on it.
  (+11, -2)(+11, -2)
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A series of robotic mining machines tunnel their way towards the lunar core, and lay conveyor systems to remove debris to the surface while reinforcing the tunnel walls.

Iron from the core is then processed to create massive shoring I-beams which keep these ever expanding caverns from collapsing as the mine-bots home in on one another to create a single chamber within an iron geodesic sphere.

Meanwhile on the lunar surface Plasma engines, shaped charges and solar sails begin to slowly increase the rotational rate of moon.

Several tens of decades go by...

The moon is now roughly twice the diameter it was when construction began and no longer has a side considered dark as it rotates twice a day.
Since no substantial mass has been added or removed from the moon, there has been no effect on the Earth's tides, though several Terran species are observed becoming spontaneously nocturnal as now even a crescent moon casts the amount of light that the full moon once reflected.

and several more decades...

It will be many years yet before enough spin has been imparted for colonists within Luna to experience one Earth gravity or 1G as centrifugal force holds them to the inner walls along the equator, but the plant life, which helps to filter and scrub the trapped atmosphere, has grown remarkable quickly. Unfettered by gravity's restraint the plants compete their way toward the central light source at a manic pace.

The main complaint of the colonists is a slight feeling of vertigo and nausea when looking across the chamber to see people miles away walking upside down above them.
These complaints have decreased substantially as the canopy has begun to fill in.

The epic Global effort to construct drive engines capable of moving an object the mass of Luna are well underway and are estimated to be ready well in advance of the last of Earth's surface vegetation and animal life dying off from our expanding Sun's increased radiation output.

The Clism of 2012 Coupled with the strict procreation laws enacted in 2126 have reduced humanity’s numbers to the point where there will be space enough for all when the Lunark embarks.

Driving around a gas giant. http://www.schlockm...nary.com/2003-08-03
See the description below the comic. [MechE, Nov 03 2015]

Some estimates http://www.sciencef...nto-a-bernal-sphere
A bit of unreviewed engineering math [CraigD, Nov 15 2015]


       // Plasma engines //   

       What's the working fluid ?   

       Apart from this, if you make it a Cube, we'll buy it. Or take it off you. Actually, that's a better option ...
8th of 7, Jul 13 2008

       Lunar rotation is phase-locked because of lunar lopsidedness. If the first portion of your project moves mass around on the moon to the point of getting it perfectly balanced, it will be much easier to get it turning.   

       Something you may want to note - if you take a uniform iron bar in space, and spin it up so that the ends are experiencing 1 g acceleration, the maximum length you can have for your iron bar is about 12000 feet - so that's about 2.3 miles diameter for the bones of the structure. Beyond that, the hanging weight of the bar is greater than its tensile strength, and it will part in the middle. Note the assumption that the ends are not supporting anything useful at all. A few hundred yards would be a realistic upper limit for an actual structure.
lurch, Jul 13 2008

       //// Plasma engines //   

       What's the working fluid ? //   

       Um, water I guess, though the space elevator should be up and running long before then to ferry up whatever would best suffice. We could also alter the course of Halley's, or sombdy elses, comet to impact the moon on a tangent in line with its rotation thus imparting spin which might otherwise take centuries to achieve and gather water to boot.   

       I did not know that the moon is lopsided. I wonder if it could be made to rotate slightly just by shifting its center of mass?   

       Aw c'mon autoboners, don'tcha want to hollow out the moon and go joyriding around the cosmos after the sun has baked the Earth?   



       I am for lunar mining as the helium 3 and other energy sources or gold may make it worth while.
travbm, Nov 02 2015

       It is my understanding that when the Mars-sized body that collided with the Earth and produced the Moon some billions of years ago, the core of that world ended up on Earth, and the Moon is mostly comprised of less-dense "mantle"-type materials. Any iron core it has will probably rather small (although of course "small", when talking about worlds, can still be pretty impressive). Just don't get hopes up, regarding how easy it is to access, and how much of it there is.
Vernon, Nov 02 2015

       If there is so much as a gold nugget in the moon I and promise you some one is going to find it. If there is a few tons of helium 3 on the moon some one is going to turn that into a profit worth more than a ton of gold.
travbm, Nov 02 2015

       Nobody seems to have figured out just how our moon formed [Vernon]. Samples supposedly show that it is roughly the same age as the Earth, but evidence of an impact large enough to have caused that much of the planet to launch are non-existent and there is no accounting for how it is receding causing many to think it formed independently.   

       My own theory is separation due to an early piriform or pear-shaped Earth with a much higher angular momentum coming into close contact, but not impact, with an extremely large body causing a lifeless and irradiated moon-sized mountain to break away.   

       Who knows for sure though?   

       [2 fries], the overall average density of the Moon is 3.34 grams/cubic-centimeter. The density of most silicate minerals is around the same value. The Earth's overall average density value is about 5.5, and about 80% of this planet is silicate minerals. The nickel-iron core is why the Earth's average density is higher than the Moon's. So, tell me again what size iron core you think the Moon has?
Vernon, Nov 03 2015

       [Vernon] I have no idea what the moon's core is comprised of. Closest I can find to an answer on the internet is;
"The composition of the lunar core is not well constrained, but most believe that it is composed of metallic iron alloyed with a small amount of sulfur and nickel. Analyses of the Moon's time-variable rotation indicate that the core is at least partly molten."

       The thrust of the idea was to hollow out the moon and give it spin so that we can colonise the equatorial interior at one Earth gravity, not mining iron.
I suppose we could chuck iron-rich asteroids at it if it turns out to be devoid of ore.

       [ ] the hollow it out and use the iron or for scaffolding paints a neat picture, but it falls apart at spinning the thing around to create -1g at the surface. Literally. It'd be like those sinkholes that appear out of nowhere and swallow entire neighbourhoods, except in this case they'd be shooting off into space.
FlyingToaster, Nov 03 2015

       Look, if we're going to go joyriding around the universe in something the size of a planet, I'm going to do it on the moon of an intact gas giant. (See link)   

       Alternatively, if I want smaller, I'm going to drill into an asteroid, put a chunk of water ice at the center and plug up the hole. Then I'm going to sit it at the focal point of a large parabolic solar mirror. Rock melts, ice converts to steam, the asteroid expands. Plug a few cracks and such and you're good to go. You could probably do that with the moon, but it's going to be a lot harder.
MechE, Nov 03 2015

       //It'd be like those sinkholes that appear out of nowhere and swallow entire neighbourhoods, except in this case they'd be shooting off into space.//   

       I'm not so sure... the mass of an expanded moon will be fighting to collapse inwards. Given spin, there will reach a point where centrifugal force and inward collapse reach equilibrium for the equatorial region.
The poles would then experience the most inward gravitational pull, and they are not needed to keep an interior atmosphere from boiling off into space.

       There would be no air-locks to breach and, at some point on a scale I don't have the math to factor, the size of the internal diameter, the centrifugal force, and one Earth gravity all line up so that not only would no sinkholes appear, much of the internal scaffolding could then be repurposed as most of it would no longer be necessary to keep the integrity of the shape.   

       The almost unthinkable part of this notion would be figuring out how to cause the Moon to one day leave Earths orbit and go tangentially-trucking off into the galaxy. We've got a billion years or so and I figured that the direction and time of departure could be nudged in a heading and toward an eventual destination of our choosing if the project were begun early enough.   

       Something like... <drifts off into daydream-land>   

       At Lagrange point one a solar reflector tracks our Moon's course and casts its shade on the lunar surface only when the Moon is travelling towards the direction of the sun and illuminating it only when it is heading away. The effect should be cumulative and able to cause the Moon to break free of the Earth's orbit given millions of years... at which point we'd probably want to slingshot the Sun to get up a head of steam.   

       I dunno, it'd make for a pretty cool sci fi series anyway.   

       The Lunark Chronicles.   

       I read in a book where they use large parabolic solar concentrators to melt spinning asteroid that they would hollow out into a trillion ton space ship.
travbm, Nov 03 2015

       Which book?   

       That was my second concept. I know John Ringo's used it, but I'm pretty sure I've read it before that, just not sure where.
MechE, Nov 03 2015

       Citadel (Troy Rising Book 2) By John Ringo was the book I was thinking about.
travbm, Nov 03 2015

       Decent author, but a rather relaxed attitude towards common sense. His "Spiral"(Helix ? something like that) had a really neat concept for a planetary system... that simply and obviously wouldn't work.
FlyingToaster, Nov 03 2015

       [+] after a fun couple of hours making some simple, ignore - all - the - material - strengh - worries mechanics estimates of the idea, which in an expression of my space geekiness, I like to call “making the Moon into a Bernal sphere”.   

       Either I made a few power of ten goofs in my arithmetic, or, to my surprise, this seemingly modest (it’s just the lil’ ole’ Moon) proposal takes borderline type II Kardeshev civilization-level engineering – assuming a 10 year spinup time, more than 10^25 W powers, about a trillion times our present civilization. Interested in details/checking my work, see [link] to my dear old science discussion site.
CraigD, Nov 15 2015

       That is so cool [CraigD]! I'm gonna print that off if you don't mind in case I someday get to learn the math.   

       It was posted as a separate idea, but I wanted to initiate both tunneling and spin by bombarding specific tangential locations on the moon by turning our land-fills into solar furnace/electro-magnetic rail-guns to convert our waste into raw materials and generate angular momentum using wave amplification.
It might take more than 400 000 000 000 times the power humanity currently uses but I think that you may have left out the factors of time and harmonically resonant amplification in microgravity.
There are other factors too but they are all strewn throughout several other postings much the same way they are scattered throughout my melon.


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